VLAN & VTP Switch Defaults (CISCO)

August 26, 2013
  • VTP server mode
  • No VTP domain name
  • VLAN 1 and VLAN’s 1002-1005 are automatically configured (cannot be deleted)
  • All access interfaces are assigned to VLAN 1 (an implied switchport access vlan 1 command)

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Posted by Josh Gahan

Creating A VLAN Step By Step

August 26, 2013

Step 1 

 a. From configuration mode, use the vlan vlan-id global configuration

command to create the VLAN and to move the user into VLAN

configuration mode.

 

b. (Optional) Use the name name VLAN subcommand to list a name

for the VLAN. If not configured, the VLAN name is VLANZZZZ,

where ZZZZ is the 4-digit decimal VLAN ID.

 

Step 2  To configure a VLAN for each access interface, follow these steps:

 a. Use the interface command to move into interface configuration

mode for each desired interface.

 

b. Use the switchport access vlan id-number interface subcommand to

specify the VLAN number associated with that interface.

 

c. (Optional) To disable trunking on that same interface, ensuring that

the interface is an access interface, use the switchport mode access

interface subcommand.

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Posted by Josh Gahan

VTP Configuration – Test Lab

August 25, 2013

Have a go at this one and see if you can find out why SW1 and SW3 do not know about each other. Be careful to read each of the switches console logs carefully to find out the answer. Answer will be up Later this week.

Network Diagram

SW1_SW3

Switch 1 – Console Log

Press RETURN to get started.
User Access Verification

Password:
SW1>enable
Password:
SW1#conf t
Enter configuration commands, one per line. End with CNTL/Z.

SW1(config)#vlan 3
SW1(config-vlan)#end
*Aug 24 13 23:13:09: %SYS-5-CONFIG_I: Configured from console by console
SW1#show vtp status

VTP Version : 1
Configuration Revision : 1
Maximum VLANs supported locally : 255
Number of existing VLANs : 6
VTP Operating Mode : Server
VTP Domain Name : FRED
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x22 0x07 0xf2 0x3a 0xf1 0x28 0xa0 0x5d
Configuration last modified by 0.0.0.0 at 8-24-2013 23:13:17
SW1#show vlan br

VLAN Name Status Ports
—- ——————————– ——— ——————————-
1 default active fa0/1, fa0/2, fa0/3, fa0/4
fa0/5, fa0/6, fa0/7, fa0/8
fa0/9, fa0/10, fa0/11, fa0/12
fa0/13, fa0/14, fa0/15, fa0/16
fa0/17, fa0/18, fa0/19, fa0/20
fa0/21, fa0/22, fa0/23, fa0/24
gi0/1
3 VLAN0003 active
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup

SW1#show int trunk

Port Mode Encapsulation Status Native Vlan
Gi0/2 on 802.1q trunking 1

Port Vlans allowed on trunk
Gi0/2 1-4094

Port Vlans allowed and active in management domain
Gi0/2 1,3

Port Vlans in spanning tree forwarding state and not pruned
Gi0/2 1
SW1#

Switch 3 – Console Log

Press RETURN to get started.
User Access Verification

Password:
SW3>show vlan br

VLAN Name Status Ports
—- ——————————– ——— ——————————-
1 default active fa0/1, fa0/2, fa0/3, fa0/4
fa0/5, fa0/6, fa0/7, fa0/8
fa0/9, fa0/10, fa0/11, fa0/12
fa0/13, fa0/14, fa0/15, fa0/16
fa0/17, fa0/18, fa0/19, fa0/20
fa0/21, fa0/22, fa0/23, fa0/24
gi0/2
1002 fddi-default act/unsup
1003 token-ring-default act/unsup
1004 fddinet-default act/unsup
1005 trnet-default act/unsup

SW3>show vtp stat

VTP Version : 1
Configuration Revision : 0
Maximum VLANs supported locally : 255
Number of existing VLANs : 5
VTP Operating Mode : Server
VTP Domain Name : fred
VTP Pruning Mode : Disabled
VTP V2 Mode : Disabled
VTP Traps Generation : Disabled
MD5 digest : 0x22 0x07 0xf2 0x3a 0xf1 0x28 0xa0 0x5d
Configuration last modified by 0.0.0.0 at 8-24-2013 23:14:47
SW3>

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Posted by Josh Gahan

VTP Pruning

August 25, 2013

By default a cisco switch flood broadcasts (and unknown destination unicast frames) in each active VLAN out all trunks, as long as the current STP topology does not block the trunk. In most campus networks, many VLANS exist only on a few switches. Therefore it’s wasteful to forward broadcasts over all trunks, causing frames to arrive at switches that do not have any ports in that VLAN.

 

Switches support two methods by which an engineer can limit which VLAN’s traffic flows over a trunk.

 

  • Manual method using the allowed VLAN list
  • VTP Pruning

 

VTP pruning allows VTP to dynamically determine which switches do not need frames from certain VLANS and then VTP Prunes those VLANs.

 

Pruning Simply means that the appropriate switch trunk interfaces do not flood frames in that VLAN.

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Posted by Josh Gahan

VLAN Database

August 25, 2013

To forward traffic for a VLAN, a switch needs to know the VLAN’s ID and it’s name and that’s the job of VTP.

The VLAN database itself is actually stored in flash as VLAN.dat 

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Posted by Josh Gahan

VLAN Trunking Protocol (VTP) – Synchronisation

August 24, 2013

Synchronisation occurs when all switches learn of a new VLAN configuration and they all learn the same VLAN ID and name.

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Posted by Josh Gahan

Visual Basic is here!

August 24, 2013

Im over 10 years late but i picked up an old Visual Basic 5 book that the local library was giving away so i decided to open it up and have a read, then i had a go at coding. I’m not the biggest fan but i can see the benefits that being able to programme yourself would have, so it’s something i will continue to work on and get better at. If you want to take a look, it’s a new menu item called “My Visual Basic Profile” from there you can access all the Visual Basic project files and even have a look at the finished EXE and see what it’s ment to do. Enjoy!

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Posted by Josh Gahan

Quick Word

August 21, 2013

Hey again,

I’m working through putting up ICND2 material now and as the weeks go on i will put alot more up.

 

I’m also in the process of creating more Router and Switch tutorial videos but until my ISP fixes my speed issues i will be holding back as it will take a verrrrry long time to upload and honestly i’m not that patient. So until then you will have alot of reading.

Til then and don’t forget to follow the blog and subscribe.

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Posted by Josh Gahan

ISL and 802.1Q Overview

August 21, 2013

ISL and 802.1Q Similarities

  • Both define a VLAN header with a VLAN ID field
  • Both support 4094 VLANS
  • Both use a 12bit VLAN header to number VLANS
  • Both support separate instances of STP for each VLAN

 

ISL and 802.1Q Differences

  • ISL is proprietary and 802.1Q is standard
  • Each use a different header
  • 802.1Q uses the native VLAN concept

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Posted by Josh Gahan

Reasons For Using VLANs

August 15, 2013
  • Create designs that allow you to group users more easily by either those working together or department
  • Allows you to segment the LAN which has the positive affect of reducing the overhead on each LAN segment
  • Provide Spanning Tree Protocol (STP) with less work to do by limiting a VLAN to an access switch
  • By keeping hosts that work together on a single VLAN, you are able to enforce stronger security by keeping the data on a individual VLAN
  • Seperate CISCO IP Phone traffic from the PC traffic

You could simplify this further:

  • Security
  • Performance
  • Design

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Posted by Josh Gahan